This invention relates to an inflation device for automobile safety equipment with a container in which a charge chamber for acceptance of a gas-producing charge and a discharge chamber with a discharge opening for connection with the safety device are provided, where a separating wall with an inside opening separates the two chambers axially from each other, which wall is connected in a fluid-tight manner with a wall of said container by interlocking connecting means.
Such inflation devices are used, for example, in connection with automobile airbags. When the gas-producing charge is ignited, the gas can flow from the charge chamber through the inside opening into the discharge chamber and from there through the discharge opening into the airbag, in order to inflate it.
Conventional inflation devices of this type are, however, in need of improvement in several regards. If, for example, such an inflation device is exposed to high exterior temperatures, as in the case of fires, the temperature rises sharply inside the container as well. This increases the ignition speed of the gas-producing charge, so that an extremely rapid rise in pressure can occur in the charge chamber when the charge is ignited. This results in the risk of the chamber or container bursting and part of the chamber being ejected at high speeds, like projectiles. There is also the risk that hot gas might enter the passenger compartment of the vehicle.
Forming the separating wall between the charge chamber and the discharge chamber of the container wall, thus connecting therewith in a fluid-tight manner through the use of interlocking connecting means, has already been proposed. As shown in FIG. 4, the container wall has previously been pressed radially inward for this purpose, in the style of a depression, so that the resultant projection on the interior of the wall penetrates into a complementary annular recess on the exterior circumference of the separating wall, i.e., the connecting means were formed as a crimp in the container wall. With this known connection, the separating wall was able to release at very high pressures in the charge chamber and move into the discharge chamber, while the gas arising in the charge chamber could flow directly through the discharge opening, i.e., without taking the detour through the inside opening in the separating wall. However, as shown in FIG. 4, the container wall expanded radially so that cracks could form in it and hot gas could escape into the passenger compartment. Furthermore, with this known connection, the pressure in the charge chamber at which the connection with the separating wall would fail could not be predicted precisely. Accordingly, there was a risk that the container rather than the separating wall would fail at some other point and burst, resulting in the problems mentioned above again.
This invention therefore relates to an improved inflation device of the type mentioned that avoids the disadvantages in the known state of the art. In particular, increased safety is to be achieved by simple means.
According to the invention, this is solved with an inflation device of the type cited at the beginning, in that the connecting means are preferably formed in the axial direction such that they fail axially when a predetermined pressure is achieved in the charge chamber, and the separating wall is movable in an axial direction in the discharge chamber.
The connecting means are therefore released at excessively high pressures in the charge chamber, free from any radial expansion of the container wall. The interlock between the separating wall and the container wall can be released by axial deformation of the connecting means so that the separating wall is released and can release the pressure in the charge chamber such that a direct connection is created between the charge chamber and the discharge opening of the discharge chamber. A theoretical deformation zone is therefore provided to achieve axial elasticity. This ensures that the gas produced always flows to the destination provided for it, i.e., through the discharge opening, and does not penetrate uncontrolled into the passenger compartment. The elasticity of the connection between the separating wall and the container wall further impedes bursting of the inflation device.
In a further development of the invention, the separating wall or the connecting means on the side of the separating wall is formed elastically. The connection between the separating wall and the container wall can be released without deformation of the container wall. This prevents the risk of cracks in the container wall. Preferably, the connecting means are formed as a flanged connection that has a container flange pointed radially inward and a separating wall flange pointed radially outward, working together with the former. Here, the separating wall flange in particular is formed elastically in the axial direction, to achieve mobility of the separating wall under excessive pressure in the charge chamber.
Preferably, the container flange can be formed in one piece with the container wall; in particular, it is formed as a embossed bead or flange in the container wall, projecting inward. Correspondingly, the separating wall flange can be formed in one piece with the separating walls; in particular it is formed as a ring-like ridge, projecting perpendicular to the axial direction at the exterior circumference of the separating wall. When the predetermined critical pressure is reached in the charge chamber, the radially-projecting separating wall flange is bent or deformed so that the separating wall can be moved axially past on the container flange. Preferably, the separating wall flange is shaped in such manner that it fails at a charge chamber pressure on the order of about 800 bars. In contrast to this, it was difficult to predict the pressure at which the connection would fail with previous separating wall connections; there was a range of variation in pressure on the order of 103 bars.
Expediently, the discharge opening of the discharge chamber has a larger cross-section than the inside opening in the separating wall. Due to the larger discharge opening, the pressurized gas can discharge rapidly. Preferably, the discharge opening and the discharge chamber are formed in the container wall and pointed radially outward. The gas flows in a radial direction outward from the container. A particularly compact arrangement of the inflation device can be achieved due to this arrangement of the discharge opening.
According to a preferred embodiment of the invention, the charge chamber is delimited on the side opposite the separating wall by an exterior wall, also placed approximately vertical to the axial direction of the container, which wall is formed separately from the container wall and connected therewith by a fluid-tight connecting means. Such an exterior wall permits the gas-producing charge to be inserted simply into the charge chamber and then to be sealed by joining the exterior wall. In a further development of the invention, the connecting means for the exterior wall are formed more rigidly than the connecting means for the separating wall, i.e., the connection for the exterior wall withstands a greater gas pressure in the charge chamber than the connecting means for the separating wall. The hot gas from the charge chamber always flows off through the discharge opening of the discharge chamber. Before reaching the resistance of the exterior wall or its connection to the container wall, the separating wall fails, so that the gas can expand through the discharge opening. The exterior wall cannot be exploded away.
Preferably a flange connection is provided for the exterior wall that incorporates an exterior wall flange, pointed radially outwards, and a container flange, pointed radially inwards, working together with the former. The exterior wall flange is more rigid and thicker than the separating wall flange.
To be able to accept the pressure in the charge chamber, the separating wall as well as the exterior wall are expediently arranged with their flanges between the related container flanges, i.e., on the side of the container flange inside the charge chamber.
According to a preferred embodiment of the invention, both the separating wall and the exterior wall are mounted in both axial directions on the container wall. The connecting means for the separating wall and the exterior wall are formed to interlock in both axial directions with the container wall. Preferably, two flanges each, in the form of radially-projecting circumferential ring-like ridges, are provided on the exterior circumference of the separating wall and the exterior wall, between which the related container flange is accepted sandwich-like. The connection can be created simply by inserting the separating wall or the exterior wall into the corresponding point in the container and pressing the container wall in from the outside at the corresponding point, which is in a ring shape, in the style of a depression, so that the bead on the inside of the container wall comes to lie between the two flanges of the separating wall or the exterior wall. The resultant connection is, for one thing, fluid-tight, and for another, has no play in the axial direction. In place of the two flanges on the separating wall or the exterior wall, an additional flange projecting inward could also be applied to the container wall, so that the corresponding separating wall flange or exterior wall flange is enclosed sandwich-like between the two container flanges. In the case of the above-described embodiment, however, fewer deformations of the container wall are necessary, which has a positive impact on its resistance.
Another preferred embodiment of the invention consists in the fact that, in addition to the charge chamber and the discharge chamber, a pressure chamber is provided for compressed gas, which chamber can be connected to the discharge chamber by means of a connecting opening. The connecting opening is first sealed fluid-tight with a releasable seal. The seal is preferably formed and arranged in such manner that it is opened by gas pressure in the charge chamber after ignition of the gas-producing charge and releases the connecting opening. To actuate the seal, a piston-cylinder unit can be provided, the piston of which is can be impinged upon by gas pressure and driven through the connecting opening. The piston here presses on the seal on the connecting opening. Preferably the seal on the connecting opening can be opened by a stopper that serves as the seal for the inside opening. This stopper can be placed in a releasable manner on or in the inside opening and seals it fluid-tight; the stopper is pressed out of the inside opening by gas pressure into the charge chamber and can be driven through the connecting opening between the pressure chamber and the discharge chamber so that it can thus open the connecting opening as well. Expediently, the inside opening is formed essentially cylindrically on the side facing the pressure chamber so that the stopper can be inserted in the style of a piston intro the inside opening.
To be able to achieve a defined, controlled collapse of the separating wall between the charge chamber and the discharge chamber with excess pressure in the charge chamber, the separating wall, in a further development of the invention, is supported on a separating wall that divides the pressure chamber from the discharge chamber. The separating wall between the discharge chamber and the pressure chamber can be formed as the floor of the container and in one piece therewith, resulting in great stability. The walls delimiting the pressure chamber are preferably formed separately and connected fluid-tight, especially welded, with the walls of the discharge chamber.
To support the separating wall between the charge chamber and the discharge chamber, a symmetrical guide is preferably provided on the longitudinal axis of the container, which guide is distanced radially from the container wall and supports the separating wall inside its fastening to the container wall. The support or guide is formed by a deformation that changes the length. It forms a deformable or damping element that is flattened upon movement of the separating wall as a result of the gas pressure in the charge chamber. A theoretical deformation zone is preferably provided for this on the guide.
To achieve a compact structure for the inflation device, the container can be formed essentially as a cylinder, particularly a circular cylinder, and the chambers can be arranged concentrically, one after the other, insider the container along the cylinder axis. The discharge chamber preferably lies between the charge chamber and the pressure chamber. The arrangement of the chambers and the openings in the separating walls between the chambers is preferably created in such manner that the gas flow from the charge chamber into the discharge chamber and the gas flow from the pressure chamber into the discharge chamber are pointed in opposition to each other.